This invention relates to an electronic thermometer for measuring body temperature, and more particularly to such a thermometer capable of outputting a warning sound with improved quality.
Since a clinical thermometer is inserted in the armpit or under the tongue to measure the body temperature, it is difficult to visually ascertain its current condition such as whether the measurement is still being taken or the measurement has been completed. For this reason, it has been known to incorporate a buzzer or the like in a clinical thermometer for acoustically outputting the condition of an electronic thermometer. In order to improve the dependability of the output, the sound wave pressure must be increased either by using a larger buzzer or applying an increased voltage to the buzzer.
In view of the manner in which clinical thermometers are used, however, their outer dimensions cannot be increased indefinitely. There is a limit beyond which the buzzer to be incorporated in a thermometer or its circuit element cannot be made larger. Thus, Japanese Patent Publication Tokko 4-30512 disclosed a circular buzzer contacting a rib inside the main housing of a thermometer so as to use the interior of the housing as a resonance chamber, Japanese Patent Publication Tokko 4-77257 disclosed a buzzer placed in an indentation prepared by making a portion of the housing structure thinner for providing a resonance space similarly as described above and making the characteristic frequency of this thinned portion of the housing equal to that of the buzzer, and Japanese Patent Publication Tokkai 61-62831 and Japanese Patent 2539224 disclosed a structure having sound-conducting routes and openings connecting the inner space and the exterior of the main housing.
One thing that is common to all these technologies is that the internal surfaces of a box-like structure is used for amplifying the sound pressure inside the resonance space and hence the construction of the box-like structure becomes complicated and/or the production process becomes cumbersome because the buzzer must be adhesively attached to the box-like structure.
Aforementioned Japanese Patent 2539224 also discloses an example whereby a resonance chamber is provided inside a buzzer unit which is separate from a box-like structure but since it is a separate unit from the module frame on which a printed circuit board (PCB) is affixed, the number of constituent parts to be assembled and hence also the number of steps in the production process are increased. Moreover, lead lines longer than the distance of separation will be required to connect the buzzer with the PCB. This will give rise to the problem of requiring a larger housing structure to contain these long lead lines as well as the problem of increased probability of breakage in the lead lines as they are bent.
If the main housing is formed with sound-conducting routes and openings, on the other hand, the inner cavity and the resonance chamber come to directly communicate to the exterior and the thermometer cannot be completely waterproofed. If one must take into consideration the possibility of the internal resonance chamber becoming invaded with water, the buzzer and the resonance chamber may have to be connected in an airtight manner in order to protect the electrical circuits. For this purpose, the entire peripheral edge of the buzzer will have to be adhesively attached to the resonance chamber, and this will allow the oscillating plate of the buzzer to vibrate only under this fixed boundary condition. As a result, only the center point becomes the point of maximum amplitude in the primary mode of oscillation, and this brings about the problem of low efficiency in the conversion to sound energy.